Decaffeination by commercial techniques often involves solvent extraction from whole green beans such as described by Patel et al. in U.S. Pat. No. 3,671,263 who use a chlorinated hydrocarbon solvent, and by Berry et al. in U.S. Pat. No. 2,309,092, who initially use a caffeine-deficient solution of coffee solubles which must then be contacted with a solvent similar to those described by Patel et al. Also of commercial importance is the extraction of caffeine from aqueous solutions with a water-immiscible solvent as described by Adler et al. in U.S. Pat. No. 2,933,395. However, each of these procedures affect the quality of the beverage.
Recently, there has been an effort made to enable the use of alternative solvents or eliminate the need for solvent/product contact. For example, in U.S. Pat. No. 4,113,886, one of us discloses that a selective membrane can be employed to effect separation. According to this patent, aqueous vegetable extracts such as those from tea or coffee are decaffeinated by causing the caffeine to diffuse through at least one porous, hydrophilic membrane and a water-immiscible solvent phase into a water phase. While this procedure does eliminate contact between the solvent and the ultimate carrier for the caffeine, namely the water phase, the rate of decaffeination is greatly limited by the relatively large surface areas required for the membranes, and the high cost of providing them.
In another approach disclosed in Belgian Pat. No. 835,556, caffeine-containing vegetable materials or extracts therefrom are contacted with liquid, water-immiscible fatty extractants at ratios of liquid extractant to caffeine solution of at least about 20:1. These high volumes of extractant seriously detract from the commercial utility of such a process. The disclosure indicates that solid vegetable materials, such as green coffee beans, can be more effectively extracted when moistened, especially when the extractant contains an amount of moisture sufficient to prevent loss of moisture from the vegetable material. It also indicates, however, that when liquid caffeine-containing extracts are to be decaffeinated, the extractant should be dried prior to contact with the liquid. Moreover, it is preferred according to that disclosure to dry the extractant after the renewal process whether solid or liquid caffeine-containing materials are being extracted. Where solid materials are being extracted, the equilibrium amount of moisture is added as fresh water in measured quantities. The disclosure further indicates that the moisture content should be kept at the lowest level necessary because non-caffeine solids are also extracted.
Thus, the prior art attempts with alternative liquid extractants and avoidance of contact between the caffeine-containing material and the extractant, present serious problems in terms of cost where production on a commercial scale is desired. Accordingly, there is a present need for improvement by means of an alternative process for decaffeination.